The subject matter disclosed herein relates to multi-energy X-ray imaging.
Non-invasive imaging technologies allow images of the internal structures or features of a patient to be obtained without performing an invasive procedure on the patient. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the observed internal features of the patient.
For example, in computed tomography (CT) and other X-ray-based imaging technologies, X-ray radiation spans a subject of interest, such as a human patient, and a portion of the radiation impacts a detector where the intensity data is collected. In digital X-ray systems a photo detector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is rotated around a patient.
In the images produced by such systems, it may be possible to identify and examine the internal structures and organs within a patient's body. It may also be desirable to characterize the tissues or agents that are present in the imaged volume, such as based on tissue type or the presence or absence of a chemical or molecule of interest, such as a contrast agent. However, in practice, such characterization may be difficult to achieve. In particular, although materials have a distinct attenuation profile as a function of energy, tissue separation in practice is not a trivial operation as tissues are a mixture of different materials with a range of densities that vary across subjects.
Such material separation may be more effectively implemented to the extent that data can be acquired at multiple, distinct energy spectra. Conventionally, systems are configured to acquire data using only two energy spectra (i.e., a high-energy spectrum and a low-energy spectrum). Material separation may, therefore, be limited to what can be achieved using two fixed spectra.
In the following description, the spectra are generally characterized by the maximum operating voltage of the X-ray tube (kVp), also denoted as the operating voltage level of the X-ray tube. Though such X-ray emissions may be generally described or discussed herein as being at a particular energy level (e.g., referring to the electron beam energy level in a tube with an operating voltage of 80 kVp, 140 kVp, and so forth), the respective X-ray emissions actually comprise a continuum or spectrum of energies and may, therefore, constitute a polychromatic emission centered at, terminating at, or having a peak strength at, the target energy.